1. Field of the Invention
The present invention is directed to a magnetic resonance apparatus and to a method for the operation of a magnetic resonance apparatus of the type having a unit for generating measured data and a unit for evaluating the measured data, wherein the measured data generating unit sends magnetic resonance raw data to the measured data evaluation unit.
2. Description of the Prior Art
For generating images with nuclear magnetic resonance, magnetic resonance signals are location-encoded with magnetic gradient fields before and during their reception. Such location encoding means that a mathematical domain known as k space is occupied with signals k space is defined by the time integral of the gradient fields. The signals in k space are then subjected to a Fourier transformation, the result of which is supplied to an image display.
The sampling of k space and the reconstruction of the images defined therewith on the basis of the acquired measured data ensue according to a fixed strategy that is defined and set before the beginning of the measurement.
In physiologically controlled measurements (for example, controlled by ECG, respiration or pulse), a time profile or template is transmitted from the measured data generating unit to the measured data evaluation unit in addition to the digitized magnetic resonance data. This information indicates the time reference of the generation of the magnetic resonance data with respect to a selected reference point of the physiological signal. The magnetic resonance data registered over many cycles of the physiological signal thus can be allocated to identical time intervals of the physiological signal in the measured data evaluation unit. This also enables the acquisition of magnetic resonance images of predominantly periodically moving subjects, which is also referred to as retrogating.
There are also methods wherein further magnetic resonance data are generated at previously defined intervals in addition to the k space data in order to control the image reconstruction therewith. Parallel to the sampling of k space for the actual image generation, thus, the data of one or more further k spaces can be acquired in time-division multiplex so that, for example, the position of the diaphragm of a patient can be recognized on the basis of the existing supplementary data. The respiration can in turn be tracked therefrom and motion artifacts can be compensated.
An object of the invention is to provide a magnetic resonance apparatus and a method for the operation of a magnetic resonance apparatus with improved measured data or image data pickup.
This object is achieved in a method and apparatus wherein the measured data generating unit sends additional control information to the measured data evaluation unit, the measured data evaluation unit sends feedback information to the measured data acquisition unit, and the feedback information influences the generation of measured data in the measured data generation unit. It is thus possible for the unit that evaluates the measured data to influence the k space sampling during the acquisition of the measured data. With such a fast feedback, having a dead time preferably below the repetition time of the sampling of the k-space rows, flexible control loops can be constructed for improving image quality. For example, a repetition of the sampling of k-space rows can be prescribed by modification of parameters until a desired quality feature such as, for example, the signal-to-noise ratio of the measured data is achieved. Another exemplary application is to control the k-space sampling in abdomen imaging or functional imaging so that motion artifacts are reduced. In another application, the measurement field is automatically shifted by an image-controlled tracking of a catheter or a biopsy needle, so that these subjects are always imaged in the middle of a graphic presentation of the examination region despite their change in position in this region.
In an embodiment, the control information is generated from a predetermined magnetic resonance measurement sequence. This measurement sequence specifies individual control information for every sampled k-space row. The additional row information is transmitted to the measured data evaluation synchronously with the measured raw data.
In a further embodiment, the control information controls the processing of the raw data of the k-space rows in the evaluation of the measured data. The raw data are supplied to an image reconstruction stage and/or to a specific data evaluation stage.
The measurement sequence can react to feedback information from the measured data evaluation at any time during the run time of the measurement. The reaction is thereby predetermined at the sequence side. In an embodiment, the feedback information is employed for the generation of the gradient control signals and/or the transmission system control signals and/or the reception system control signals. The reaction time thereby preferably lies below the typical repetition time of the sampling of the k-space row, i.e. the time that is required for generating the data for a k-space row.
The data channel from the measured data evaluation to the measured data generating unit is fashioned such that, in addition to a high bandwidth, for example 100 MB/s, a slight and deterministic dwell or delay time, is guaranteed in the data transmission, for example on the order of magnitude of 4 through 4 Ms.